The present invention concerns the preparation of dental workpieces and more particularly the preparation of workpiece models for denture parts such as crowns or bridges or for workpieces which form directly the denture part, for example, crowns, bridges or facings.
Customarily, in the preparation of dentures, initially a lost wax molding pattern is prepared; it corresponds in its shape to the denture to be made (positive pattern), whereupon with the lost molding pattern, a hollow mold (negative pattern, for example of gypsum) is produced, in which the denture is finally cast.
The molding of such workpieces in an articulator is time consuming and difficult, even if lost patterns made of wax are utilized.
To facilitate the work, semifinished parts in numerous configurations and materials are available. These are in most cases platelets representing the biting surface, which must be backed with supporting material until the workpiece encompasses the stump of the tooth and then shaped in keeping with the articulation movements.
Semifinished parts of this type must therefore be well deformable for further shaping, and adaptation and for this reason usually consist of a wax which is soft and subject to the risk of smearing. Furthermore, semifinished parts made of wax are hardly applicable in the case of minimal space conditions in the area of the chewing surfaces, i.e. when the distance between the tooth stump and the counter biting surface is small. The reason for this is the fact that with a wall thickness of less than 0.5 mm, the semifinished model is no longer stable and may be completely deformed.
If, on the other hand, the semifinished part of a stronger synthetic plastic material is utilized, such as for example described in German Patent DE-OS No. 2 257 724, moldability and adaptation to the individual conditions of the patient are strongly restricted. Frequently the model cannot be molded, but must be machined, i.e. ground.